1. Field of the Invention
The present invention relates to a photographic exposure determining apparatus and a film type data processing apparatus for use in a photographic printer. In particular, the present invention relates to an apparatus for determining the exposure for photographic printing, that is capable of automatically determining, on the basis of a reference printing exposure condition, the correct exposure condition with respect to each of a plurality of film types; and also to an apparatus for processing data on film types that is used in a photographic printer and is capable of automatically determining the correct exposure condition in the above-described manner with respect to each of a plurality of film types, to process data on film types.
2. Description of the Related Art
An image formed on a color negative allows, on the whole, the transmission therethrough of light of three colors, i.e., blue (B), green (G), and red (R). It is known from experience that, as a rule, the transmittance values of these three color-components are substantially equal to one another, or in a fixed ratio to each other. From this fact, an automatic photographic printer determines a printing light quantity (i.e., exposure) on the basis of the following formula: EQU Log Fj=Kj+Dj . . . (1)
where log F represents the logarithm of the printing light quantity, K represents a constant, D represents the light accumulated transmission density (LATD) measured by a photometric system, and j stands for any of B, G, and R light.
However, when the printing light quantity is controlled by an automatic photographic printer on the basis of the above-stated formula (1), the following problem arises. A print produced from an underexposed negative has an overall high density, whereas a print produced from an overexposed negative has a low density. In order to cope with this problem, a slope control circuit is provided to correct the term Dj in the formula (1) before the exposure is finally determined. However, even with an automatic printer provided with this slope control circuit, defective prints having incorrect color balance may be produced when the negative used is, for instance, a negative whose properties have changed due to the passage of a long period of time, a negative subjected to photographing using a light source much different from daylight, such as a fluorescent lamp or a tungsten lamp (i.e., a heterogeneous light-source negative), or a negative suffering from color failure. In addition, when it is necessary to process heterogeneous films, i.e., films manufactured by different manufactures, or films having differing sensitivities, because the three photosensitive layers of such heterogeneous films have different sensitivities, densities, etc., it is impossible to produce good prints under the same printing condition. Accordingly, the printing condition is determined with respect to each of the various different film types by trial and error before printing is affected. Thus, during the determination of the exposure, the term Dj of the formula (1) is corrected (this procedure is called "color correction"). If heterogeneous films are to be processed, another procedure takes place where the slope control value is varied.
In recent years, many types of high-sensitivity films have been produced, and the number of film types available has increased to several tends of types. However, as described before, the printing exposure conditions required by a plurality of film types are not always the same. In addition, although condition setting films are used to set the condition of the automatic printer with respect to each of various different film types, they cover only a very limited number of film types, which may serve as reference film types. Normally, a condition setting film is a negative having a first portion corresponding to a negative on which an image of a gray object is formed by photographing, and a second portion disposed around the first portion and corresponding to a negative on which an image of a yellow-green object is formed by photographing. Three kinds of condition setting films, i.e., a correct exposure negative, an underexposed negative, and an overexposed negative are available with respect to one reference film type. However, with respect to those film types whose characteristics differ from those of reference film types, the printing exposure conditions have to be set based on experience. In this way, the setting of a printing exposure condition with respect to each of various different film types is very difficult and requires experience accumulated over a long period of time. Further, in order to maintain high print quality, it is essential to suitably manage the printing exposure conditions with respect to each of various different film types. However, this management is difficult when there are many film types. To cope with this problem, the following techniques have been proposed, in which the correct exposure to be used during printing with respect to each of various film types is automatically determined on the basis of a single reference condition for printing exposure.
Japanese Patent Laid-Open No. 62-85235 (1987) discloses a method in which a correction amount for correcting a printing exposure condition for a reference film is stored in a memory in correspondence with each of several film types. The film type of a film to be subjected to printing is determined by reading a bar code (the so-called DX code) recorded on the film. The correction amount corresponding to the determined film type is read to determine the exposure. With this method, however, since the correction amount has to be obtained before printing in correspondence with each of various film types, a great amount of labor is required and the level of precision achievable is insufficient when film types widely vary as they do nowadays. Furthermore, when a new film type is to be processed, a new correction amount has to be set. For this purpose, data on film codes have to be stored in the memory in correspondence with various film types. It is a very cumbersome task to manage a large number of film types, or to manage the addition of a new film type or the withdrawal of an obsolete film type.
Japanese Patent Laid-Open Nos. 51-94927 (1976), 52-20024 (1977), 59-220761 (1984), 61-198144 (1986), etc. disclose techniques to divide a film frame into a plurality of sections, measure light with respect to each of the sections, and to subsequently analyze items of data obtained by the measuring of light (i.e., the photometric values), and correct a reference printing exposure condition on the basis of a selected photometric value so as to determine the exposure condition for use in printing of a film image which is to be printed. According to this known art, if the spectral sensitivity distribution in the light-measuring portion of the photometric system of the automatic printer accords with that of a printing photosensitive material with a very high degree of precision, it is possible to subject a plurality of types of films having different characteristics, to printing on the basis of the printing exposure condition corresponding to a reference film type.
If such is the case, i.e., if the spectral sensitivity distribution of the photometric system accords with that of the exposure portion, it is possible to effect correct printing exposure with respect to each of several film types on the basis of the printing exposure condition for the reference film type, only when the following condition is simultaneously satisfied. That is, the linear portions of three curves representing the characteristics of the relevant film with respect to R, G and B lights are substantially parallel to the linear portions of three curves representing the characteristics of the reference film type. For this reason, the above-described known art fails to produce good printed images within the exposure region that corresponds to the non-linear portions of the characteristic curves. Furthermore, in order to select photometric data, a certain reference value (e.g., a neutral color value) is necessary. It is an essential requirement that this reference value is correct.
In order to obtain the correct reference value, a method is known in which the reference value is determined using photometric data on images of one whole film. However, when the majority of images in one film are images deviating from standard images, the resultant reference value will also deviate, thereby leading to an error in the selection of the photometric data. When there are only a small number of image frames on the film, and, accordingly, only a small number of items of photometric data is available, the resultant reference value will have a low level of accuracy.
In order to overcome the above-mentioned problems, it is necessary to classify a plurality of films of various different types according to their film types by reading the bar codes recorded on the films. Also, data on the image density of a relatively great number of film images is stored with respect to each of the film types, and the above-described reference value is calculated on the basis of the image density. However, this would lead to the problem that, as the number of film types increases, the number of items of data also increases, thereby resulting in a shortage of storage capacity.